1. Field of the Invention
The present invention relates generally to H.323 telecommunications networks, and specifically to call routing within an H.323 network.
2. Background of the Present Invention
Local Area Networks (LANs) not only interconnect computers for data communications, but can also interconnect terminals (hereinafter termed endpoints) for voice communications. For example, many LANs are now implementing H.323 architecture to provide multimedia communications services over LANs. H.323 endpoints may be integrated into personal computers, implemented in stand-alone devices, such as wireline or wireless telephones or implemented in wireless telecommunications systems. H.323 endpoints can provide real-time audio, video and/or data communications capabilities in point-to-point or multipoint conferences.
Within an H.323 system, each H.323 endpoint is registered with a Gatekeeper for the H.323 system. The Gatekeeper stores an Internet Protocol (IP) address for the H.323 endpoint, so that when a connection to that H.323 endpoint is requested, the Gatekeeper knows how to route the connection. If the H.323 endpoint is a Mobile Station (MS), such as a cellular telephone, the IP address for the MS typically includes the IP address for a Mobile Switching Center (MSC) serving the MS along with a specific port number for that MS. Therefore, although each MS has a separate subscriber record within the Gatekeeper, each MS has the same IP address, e.g., the IP address of the MSC. In addition to the routing information, the Gatekeeper also stores the permanent subscriber information for the MS.
The protocol used by the Gatekeeper to communicate with the H.323 endpoints for call control purposes is the H.225 protocol. Today, if a call to an H.323 endpoint needs to be re-directed from that H.323 endpoint to another H.323 endpoint or to a terminal outside the H.323 system, the H.225 protocol uses a Facility message to handle re-direction of the call. However, the Facility message requires the H.323 endpoint originally receiving the call to know the new number (IP address for the other H.323 endpoint or directory number for the other terminal) in order to re-direct the call.
For example, when a call is originated to an MS within the H.323 system from a calling party outside of the H.323 system, the called party number for the called MS is typically an xe2x80x9coffice numberxe2x80x9d similar to a private branch exchange number that identifies the Gatekeeper of the H.323 system. Therefore, even if the MS has roamed outside of the H.323 system into the Public Land Mobile Network (PLMN), calls to the MS will still come into the Gatekeeper. Since the Gatekeeper only stores internal H.323 routing information, these calls will be routed to the MSC within the H.323 system that was previously serving the MS before the MS roamed outside of the H.323 system. However, since the MS 20 has roamed outside of the H.323 system, when the MSC attempts to page the MS, these paging attempts will fail.
In order to complete the call to the MS, the call must be re-directed to the PLMN. Although the MSC within the H.323 system could store the Mobile Station Integrated Services Digital Network (MSISDN) number of the MS, which is the number required by the PLMN to reach the MS, this is not a desirable or efficient solution. In order to re-route calls to the MS using the existing H.225 protocol, the MSC would have to store the MSISDN number of each MS that it serves and send this MSISDN number to the Gatekeeper in the Facility message.
The present invention is directed to telecommunications systems and methods for re-directing failed calls to H.323 endpoints within an H.323 system by adding a unique re-routing release cause to a Release Complete message in the H.225 protocol that indicates that the call should be re-routed to another number. The Gatekeeper stores the alternative number for the H.323 endpoint, and upon reception of this re-routing cause in the Release Complete message, the Gatekeeper establishes a new leg of call to the alternative number. Since the Gatekeeper already stores routing information for H.323 endpoints, the Gatekeeper has the capability to store alternative numbers as well. Storing the alternative number in the Gatekeeper furthers the functionality of the Gatekeeper in directing and re-directing calls in the H.323 system.